//使用define宏函数
#include <stdio.h>
#define pingjun(x,y) (2.0*x*y)/(x+y)
int main(void)
{
	printf("%d     %d      %f", 25, 32, pingjun(25, 32));
	return 0;
}
//以下是标答；
#include <stdio.h>
#define HMEAN(X,Y) (2.0 * (X) *(Y) / ((X) + (Y)))
int main(void)
{
 double x, y, ans;

 puts("Enter a pair of numbers (q to quit): ");
 while (scanf("%lf %lf", &x, &y) == 2)
 {
 ans = HMEAN(x,y);
 printf("%g = harmonic mean of %g %g.\n", ans, x, y);
// see if works with arithmetic expressions
 ans = HMEAN(x + y, x * y);
 printf("%g = harmonic mean of %g %g.\n", ans, x + y, x * y);
 puts("Enter a pair of numbers (q to quit): ");
 }
 puts("Bye");

 return 0;
}